Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

**-s**- Check the spatial topology of temporally related maps and select only spatially related maps
**-d**- Perform a dry run, compute all dependencies and module calls but don't run them
**--help**- Print usage summary
**--verbose**- Verbose module output
**--quiet**- Quiet module output
**--ui**- Force launching GUI dialog

**type**=*name*- Type of the input space time dataset
- Options:
*strds, stvds, str3ds* - Default:
*strds* **expression**=*expression***[required]**- The temporal mapcalc expression

`"result = expression"`

The statement structure is similar to r.mapcalc, see r.mapcalc.
Where **result** represents the name of a space time dataset
(STDS)that will contain the result of the calculation that is given as
**expression** on the right side of the equality sign.
These expression can be any valid or nested combination of temporal
operations and functions that are provided by the temporal algebra.

The temporal algebra works with space time datasets of any type
(STRDS, STR3DS and STVDS). The algebra provides methods for map
selection from STDS based on their temporal relations. It is also
possible to temporally shift maps, to create temporal buffer and to
snap time instances to create a valid temporal topology. Furthermore
expressions can be nested and evaluated in conditional statements (if,
else statements). Within if-statements the algebra provides temporal
variables like start time, end time, day of year, time differences or
number of maps per time interval to build up conditions. These
operations can be assigned to space time datasets or to the results of
operations between space time datasets.

The type of the input space time datasets must be defined with the input
parameter **type**. Possible options are STRDS, STVDS or STR3DS.
The default is set to space time raster datasets (STRDS).

As default, topological relationships between space time datasets will be
evaluated only temporal. Use the **s** flag to activate the
additionally spatial topology evaluation.

The expression option must be passed as **quoted**
expression, for example:

t.select expression="C = A : B"

equals A ------ B ------ during A ---- B ------ contains A ------ B ---- starts A ---- B ------ started A ------ B ---- finishs A ---- B ------ finished A ------ B ---- precedes A ---- B ---- follows A ---- B ---- overlapped A ------ B ------ overlaps A ------ B ------ over booth overlaps and overlapped

Topological relations must be specified in {} parentheses.

LEFT REFERENCE l Use the time stamp of the left space time dataset INTERSECTION i Intersection DISJOINT UNION d Disjoint union UNION u Union RIGHT REFERENCE r Use the time stamp of the right space time dataset

C = A : B

In addition the inverse selection operator **!:** is defined as the
complement of the selection operator, hence the following expression

C = A !: B

To select parts of a STDS by different topological relations to other STDS,
the temporal topology selection operator can be used. The operator consists of
the temporal selection operator, the topological relations, that must be separated
by the logical OR operator **|** and the temporal extent operator.
All three parts are separated by comma and surrounded by curly braces:

{"temporal selection operator", "topological relations", "temporal operator"}

C = A {:, equals} B C = A {!:, equals} B

C = A {:,equals|during|overlaps} B

In addition we can define the temporal extent of the result STDS by adding the temporal operator.

C = A {:, during,r} B

The selection operator is implicitly contained in the temporal topology selection operator, so that the following statements are exactly the same:

C = A : B C = A {:} B C = A {:,equal} B C = A {:,equal,l} B

C = A !: B C = A {!:} B C = A {!:,equal} B C = A {!:,equal,l} B

Note A and B can either be space time datasets or expressions. The temporal relationship between the conditions and the conclusions can be defined at the beginning of the if statement. The relationship between then and else conclusion must be always equal. if statement decision option temporal relations if(if, then, else) if(conditions, A) A if conditions are True; temporal topological relation between if and then is equal. if(conditions, A, B) A if conditions are True, B otherwise; temporal topological relation between if, then and else is equal. if(topologies, conditions, A) A if conditions are True; temporal topological relation between if and then is explicit specified by topologies. if(topologies, conditions, A, B) A if conditions are True, B otherwise; temporal topological relation between if, then and else is explicit specified by topologies.

Symbol description == equal != not equal > greater than >= greater than or equal < less than <= less than or equal && and || or

td(A) Returns a list of time intervals of STDS A start_time(A) Start time as HH::MM:SS start_date(A) Start date as yyyy-mm-DD start_datetime(A) Start datetime as yyyy-mm-DD HH:MM:SS end_time(A) End time as HH:MM:SS end_date(A) End date as yyyy-mm-DD end_datetime(A) End datetime as yyyy-mm-DD HH:MM start_doy(A) Day of year (doy) from the start time [1 - 366] start_dow(A) Day of week (dow) from the start time [1 - 7], the start of the week is Monday == 1 start_year(A) The year of the start time [0 - 9999] start_month(A) The month of the start time [1 - 12] start_week(A) Week of year of the start time [1 - 54] start_day(A) Day of month from the start time [1 - 31] start_hour(A) The hour of the start time [0 - 23] start_minute(A) The minute of the start time [0 - 59] start_second(A) The second of the start time [0 - 59] end_doy(A) Day of year (doy) from the end time [1 - 366] end_dow(A) Day of week (dow) from the end time [1 - 7], the start of the week is Monday == 1 end_year(A) The year of the end time [0 - 9999] end_month(A) The month of the end time [1 - 12] end_week(A) Week of year of the end time [1 - 54] end_day(A) Day of month from the start time [1 - 31] end_hour(A) The hour of the end time [0 - 23] end_minute(A) The minute of the end time [0 - 59] end_second(A) The second of the end time [0 - 59]

The structure is similar to the select operator with the extension of an aggregation operator: {"comparison operator", "topological relations", aggregation operator, "temporal operator"}

This aggregation operator (| or &) define the behaviour if a map is related the more than one map, e.g for the topological relations 'contains'. Should all (&) conditions for the related maps be true or is it sufficient to have any (|) condition that is true. The resulting boolean value is then compared to the first condition by the comparison operator (|| or &&). As default the aggregation operator is related to the comparison operator:

Comparison operator -> aggregation operator:

|| -> | and && -> &

Condition 1 {||, equal, r} Condition 2 Condition 1 {&&, equal|during, l} Condition 2 Condition 1 {&&, equal|contains, |, l} Condition 2 Condition 1 {&&, equal|during, l} Condition 2 && Condition 3 Condition 1 {&&, equal|during, l} Condition 2 {&&,contains, |, r} Condition 3

A{#, contains}B

A list of integers (scalars) corresponding to the maps of A that contain maps from B will be returned.

C = if({equal}, A {#, contains} B > 2, A {:, contains} B)

Furthermore the temporal algebra allows temporal buffering, shifting and snapping with the functions buff_t(), tshift() and tsnap() respectively.

buff_t(A, size) Buffer STDS A with granule ("1 month" or 5) tshift(A, size) Shift STDS A with granule ("1 month" or 5) tsnap(A) Snap time instances and intervals of STDS A

tmap()

C = A {:,during} tmap(event)

D = if(start_date(A) < "2005-01-01", A : B : C)

D = if(A {#, contains} B > 3, A {:, contains} B, C)

D = if(contains, td(buff_t(A, "1 days")) == 3, B, C)

Gebbert, S., Leppelt, T., Pebesma, E., 2019. A topology based spatio-temporal map algebra for big data analysis. Data 4, 86. https://doi.org/10.3390/data4020086

Available at: t.select source code (history)

Latest change: Thu Apr 15 15:26:30 2021 in commit: c81d87a6a99b34ba2528f6041ee21468968a3a35

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

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